I. Field of the Invention
This invention relates to the field of liquid metering systems and such systems for collecting, metering and monitoring liquids, and more particularly, to an electronically controlled liquid meter or monitor assembly that has particular use in the medical field for collecting, metering and monitoring a body fluid from a living organism, such as urine, which assembly has improved accuracy by including the ability to substantially inhibit any influence on weight determination of the amount of liquid collected due to movement by the living organism.
II. Description of the Prior Art
There are many known devices and systems for the collection and taking of physical measurements or metering of body fluids. In, for example the medical field, in many instances of patient treatment it is often necessary to know at all times the accurate amount of body fluid, such as urine, that is being passed by the patient. It is, in fact, rather conventional in hospitals to collect urine from patients for the measuring and monitoring of urine output as is routinely done for post-operative patients as well as those with urological disorders where, for example, urine output is directly related to renal function. This type of procedure for collecting, measuring and monitoring urine takes on extreme importance because, for example, sudden changes in urine flow, which can occur at any time, can indicate that there is a deteriorating clinical condition in the patient. Changes in urine output have been correlated with changes in cardiac output.
The collection of urine output is typically accomplished by first catheterizing the patient, i.e. a catheter is first passed through the urethra of the patient and the other end of the catheter is connected to a container or drainage bag through a length of flexible tubing. Typically the bag is supported below the patient from the patients bed or other support system, and urine drains by gravity from the patient through the flexible tubing and into the bag.
The prior art describes many different types of systems which are employed to collect and measure urine output. For example, many of the systems use urine collection bags formed of a clear and flexible plastic material which contain indicia in the form of graduations on the bag itself that represents the volume of the urine in the bag. In other systems the urine collection receptacle includes a rigid and clear plastic reservoir in fluid communication with a collection bag which reservoir has volume related indicia and into which the urine initially flows and is stored prior to being emptied into the bag. See, for example, the urine meter bag described in U.S. Pat. No. 4,305,405. Both of these devices present several disadvantages. For example, there is definitely a lack of accuracy in obtaining measurement readings that are made using the printed indicia and there is often a degree of difficulty in reading these devices depending on where they are positioned. Furthermore, the urinary output measurements and monitoring is dependent upon a person coming at precise time intervals to obtain and record the measurements. This is often difficult to do. In addition, the bags with reservoirs require someone to empty the reservoir so that it has room to fill again with urine.
There are many other types of mechanical, electromechanical, and electronic devices used for metering, monitoring and/or collecting body fluids, such as urine. Aside from many of these devices lacking a certain degree of accuracy, they often present problems dealing with safety, high cost to manufacture and/or to operate, lack of portability and general difficulty to use. However, regarding accuracy, many of these systems are often confronted with the inaccurate measurements regarding the amount of urine collected due to the influence of patient movement on the measuring or weighing device used within the system. This is particularly true because the patient is generally connected to the weighing device by flexible tubing. See, for example, the systems described in U.S. Pat. Nos. 4,343,316, 4,390,073, 4,417,585 and 4,448,207 and the article in Medical and Biological Engineering, November, 1976, on pages 665-670 entitled "Instruments for Sampling and Measuring the Volume Output of Urine from Grazing Female Sheep" by Chambers et al.
It is also known in urine output measurement systems to use an ultrasound measurement technique for determining the height of a column of urine in a rigid walled container and deducing from that height the volume of the liquid.